5/10/2021 1 Welcome to Clinical anatomy of the head, neck and neuronal pathways Lecture #11 Department of Anatomy MUNI, MED Alemeh Zamani, Ph.D. Spring 2021 Today’s lecture will cover: 1- Pathways of Somatomotor System 2- Connections of the Cerebellum and Basal Ganglia 3- Spinal Reflex Motor 4- Eye Movement Pathways of Somatomotor System Necessary components of proper motor control o Volition o Coordination of signals to many muscle groups o Proprioception o Postural adjustments o Sensory feedback o Compensation for the physical characteristics of the body and muscles o Unconscious processing o Adaptability Levels of Movement Regulation o Spinal cord o Brain stem o Cortex o Cerebellum o Basal ganglia Lower Motor Neurons – Spinal Cord o α motoneurons: innervate the extrafusal muscle fiber o γ motoneurons: innervate intrafusal muscle fibers o Somatotopic organization o medial column – axial muscles o lateral column – limb muscles o anteriorly – extensors o posteriorly - flexors Lower Motor Neurons – Brain Stem Monkhouse, Cambridge: Cambridge University Press 2005 5/10/2021 2 Supraspinal System of Movement Control o Medial system ▪ bilateral ▪ terminates on the interneurons or the medial column of lower motor neurons ▪ controls maintenance of balance and postural movements o Lateral system ▪ mostly cross the midline and descend contralaterally ▪ terminates on the interneurons or the lateral column of lower motor neurons ▪ controls fine manipulative movements of the hand and fingers Medial System o Cortical pathways ▪ Anterior corticospinal tract medial column of lower motor neurons o Subcortical pathways ▪ Medial and lateral vestibulospinal tracts control of balance and postural movements, head movements ▪ Tectospinal tract (sup. colliculus) coordination of movements of the head and eyes during watching ▪ Medial (pontine) and lateral (medullary) reticulospinal tracts control of postural movements Lateral System o Cortical pathways ▪ Lateral corticospinal tract o Subcortical pathways ▪ Rubrospinal tract (Red nucleus of mid brain) contralaterally descends to the lateral column facilitatory to flexors of upper limb Corticospinal tract and Corticonuclear Tracts voluntary movements of the body Corticospinal Tract (or Pyramidal Tract) originates in the motor cortex form the medullary pyramids at the level of the medulla 90% of the axons cross over to the contralateral side at the pyramidal decussation, forming the lateral corticospinal tract (lateral funiculus of the spinal cord)- responsible for the control of the distal musculature 10% of the axons (anterior corticospinal tract-anterior funiculus) cross over to the contralateral side through the anterior white commissure- responsible for the control of the proximal musculature terminate in the contralateral (and to some ipsilateral and some bilateral) motor nuclei of the cranial nerve Corticonuclear tract Corticospinal tract and Corticonuclear Tracts voluntary movements of the body • somatomotore - ncl. CN. III., IV., VI., XII • branchiomotore - ncl. CN. V., VII., IX., X Motor Cortex 5/10/2021 3 Connections of the Cerebellum and Basal Ganglia Cerebellum Functions: o Maintenance of balance and equilibrium o Muscle tone o Coordination of voluntary movements o Motor learning Damage to cerebellum: Inability to maintain the equilibrium of the body Difficulty to touch his nose with a finger Unable to fix the gaze on an object Cerebellum Anatomical Division Connections of the Vestibulocerebellum Vestibular system Flocculonodular lobe (vestibulocerebellum) Vestibular ncll. Spinal motor neuronsVestibulospinaltracts ➢ vestibular reflexes ➢ postural maintenance Vestibulocerebellartract Connections of the Spinocerebellum – Median Zone Vermis (spinocerebellum) Vestibular ncll. Spinal motor neurons Bulbocerebellartract Cuneocerebellartract Spinocerebellartracts Vestibulospinaltracts Ncl. fast. FR Reticulosp.tracts Th. VL MC Ant.corticoospinaltract ➢ control of medial descending (motor) system Connections of the Spinocerebellum – Paramedian Zone Intermediate zone (spinocerebellum) Spinal motor neurons Bulbocerebellartract Cuneocerebellartract Spinocerebellartracts Ncll. emb.+ glob. RN Rubrosp.tract Th. VL MC Lat.corticoospinaltract ➢ control of lateral descending (motor) system 5/10/2021 4 Connections of the Cerebro (ponto)-Cerebellum – Lateral Zone Lateral zone (pontocerebellum) Spinal motor neurons Pontocerebellar tract Ncl. dentatus Pontine ncll. Th. VL Motor cortex Lat.corticoospinaltract ➢ planning and timing of movements ➢ cognitive functions Corticopontinetract Ataxia - errors in the force, direction, speed and amplitude of movements, loss of coordination Dysmetria - „overshooting or undershooting“ - the hand may travel past the target Hypotonia - decreased muscle tone Adiadochokinesia - inability to perform rapid alternating movements Intention tremor - involuntary movement caused by alternating contractions of opposing muscle groups Cerebellar Disorders Basal Ganglia o Caudate nucleus o Lentiform nucleus (putamen and the globus pallidus) o Substantia nigra o Ncl. subthalamicus Basal Ganglia Connections Connections o Direct pathway o Indirect pathway o Nigrostrital pathway Transmitters o Glutamate: corticostraital & thalamostrital o GABA: striatopallidal & pallidothalamic o Dopmanie: nigrostrital pathway Cerebral Cortex Striatum Thalamus Globus Pallidus Subthalamic n. Substantia Nigra Basal Ganglia Connections Transmitters o Glutamate o GABA o Dopmanie Cerebral Cortex Striatum Thalamus –VA & VL GP ext GP int Subthalamic n. Substantia Nigra Basal Ganglia Connections- Direct Pathway Initiation of motor movement 5/10/2021 5 Transmitters o Glutamate o GABA o Dopmanie Cerebral Cortex Striatum Subthalamic n. Substantia Nigra Basal Ganglia Connections- Indirect Pathway GP ext GP int Thalamus –VA & VL Stopping unwanted movement Cerebral Cortex Striatum- D2 Thalamus Globus Pallidus Subthalamic n. Substantia Nigra Basal Ganglia Connections- Nigrostrital Pathway Cerebral Cortex Striatum- D1 Thalamus Globus Pallidus Substantia Nigra Spinal Reflex Motor o Type of afferents ▪ somatic spinal reflexes ▪ visceral spinal reflexes o Type of somatosensor ▪ proprioceptive reflexes ▪ exteroceptive reflexes o Number of involved spinal segments ▪ monosegmental spinal reflexes ▪ polysegmental spinal reflexes o Number of synapses ▪ monosynaptic reflexes ▪ disynaptic reflexes ▪ polysynaptic reflexes Intrafusal muscle fibers are proprioceptors Innervated by gamma motorneurons Extrafusal muscle fibers generate movement Innervated by alpha motorneurons Skeletal Muscle Structure Spinal Reflex Reflexes with their reflex center in the spinal cord are called spinal reflexes. Structural components: o A receptor o An afferent neuron o A reflex center o An efferent neuron o An effector Myotatic (stretch) reflex Withdrawal (flexion) reflex Spinal Reflex 5/10/2021 6 Myotatic (Stretch) Reflex Receptors for the stretch reflex are the muscle spindles. Myotatic (Stretch) Reflex Reflex loop of Golgi tendon organ (inverse myotatic reflex) Withdrawal (Flexion) Reflex Receptors for the flexion reflex are nociceptors. Motorneurons can inhibit their own activity by Renshaw Cells! A negative feedback loop to stabilize the motorneurons Gamma Loop muscle spindle intrafusal muscle fibres Ia afferent gamma motoneurons alpha motoneurons extrafusal muscle fibres descending pathways (FR) Critical for maintenance of stretch reflexes and muscle tone Eye Movement o Eye movements ▪ conjugate – both eyes in same direction ▪ vergent - during motion of object to and from us ➢ convergent ➢ divergent 5/10/2021 7 Conjugate Movements Eye Movement Pathways o Saccades Rapid eye movements, conjugated movement, voluntary or involuntary o Smooth pursuit movements Follows moving visual target, voluntary o Vestibulo-ocular movements Initiated by vestibular mechanisms during brief/rapid head movement o Vergence movements Adjusts for different viewing distance Saccadic Eye Movements o horizontal gaze center – PPRF, abducens lower motor neurons and interneurons o Vertical gaze center located at RF of the midbrain, lower motor neurons in the oculomotor and trochlear nuclei Neurons in the frontal eye field Superior colliculus neurons Correct and send control signals vertical and horizontal gaze centers ➢ superior colliculi – information from retina, auditory, and parietal (visual association) area Nuclei of the basal ganglion: superior colliculus/caudate/substantia nigra voluntary and memory-guided saccades reflex orienting saccades Smooth Pursuit Movements Temporal eye field neurons/ Frontal eye field neurons Dorsolateral pontine nucleus Contralateral cerebellum Vestibular nuclei Medial longitudinal fasciculus : CN III, IV, VI Vestibulo-Ocular Movements Vestibular mechanisms during head movement Vestibular Receptors & Vestibular 1° Afferent Neurons Horizontal Movements: Medial Vestibular Nucleus Vertical Movements: Superior Vestibular Nucleus Gaze Stabilization Vergence Movements Supraoculomotor nuclei Visual system including visual association cortex CN III, Medial rectus muscles Gaze Shifting 5/10/2021 8 Reading List Thank you very much for your attention